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Dopamine enhances expectation of pleasure in humans

Enhancing the effects of the brain chemical dopamine
influences how people make life choices by affecting expectations of pleasure, according
to new research from the UCL Institute of Neurology.

The study, published today in Current Biology, confirms an important role for dopamine in how human
expectations are formed and how people make complex decisions. It also contributes
to an understanding of how pleasure expectation can go awry, for example in
drug addiction.

Dopamine is a neurotransmitter produced in several areas of
the brain that is found in a wide variety of animals. Its role in reward learning
and reward-seeking behaviour is well established by animal studies – however, in
humans its role is much less understood.

Lead author Dr Tali Sharot, Wellcome Trust Centre for
Neuroimaging at UCL, said: “Humans make much more complex decisions than other
animals – such as which job to take, where to go on holiday, whether to start a
family – and we wanted to understand the role of dopamine in making these types
of decisions. Our results indicate that when we consider alternative options
when making real-life decisions, dopamine has a role in signalling the expected
pleasure from those possible future events. We then use that signal to make our
choices.”

The research team, which included Dr Tamara Shiner and
Professor Ray Dolan, examined estimated pleasure of future events before and
after the administration of a drug called L-DOPA which is known to enhance
dopamine function in the brain and is commonly used to treat patients with
Parkinson’s disease. The 61 study participants were asked to rate their expectations
of happiness if they were to holiday at each of 80 destinations, from Thailand to Greece. They were then given L-DOPA
or a placebo and asked to imagine holidaying in those destinations.

The following day participants had to pick between a series
of paired destinations that they had initially assigned with equal ratings, one
member of the pair was imagined under L-DOPA the day before and the other under
placebo. Finally, they rated the full set of 80 destinations again.

Ratings for particular destinations increased after they
were imagined under L-DOPA’s influence. That increase also affected the
participants’ selections the following day. Dr Sharot added: “We had reason to
believe that dopamine would enhance expectations of pleasure in humans, but
were surprised at the strength of this effect. The enhancement lasted at least
24 hours and was evident in almost 80 per cent of the subjects.”

The study builds on earlier work by Dr Sharot and colleagues,
which used brain imaging as participants imagined holiday destinations. An area
of the brain called the striatum tracked expectations and the scientists found
that they could take that signal and predict what the participants would
choose. The authors believed this was dopamine at work and set up this study to
further explore its role.

UCL context

Wellcome Trust Centre for Neuroimaging at UCLThe
Functional Imaging Laboratory (FIL) was founded in 1994 following a
major grant award from the Wellcome Trust. In 2006, following a
successful bid for a Strategic Award the laboratory was awarded
Wellcome Trust Centre status and given its current name.

UCL Neuroscience brings together over 400
senior investigators who conduct world-leading research in molecular,
developmental, cellular, cognitive, computational, and clinical
neuroscience. The inter-disciplinary department has a particular
strength in translating its research into new ways of diagnosing and
treating disease through its partnerships with three large
comprehensive and specialist biomedical centres.